This invention relates to electrical circuit breakers.
Present circuit breakers generally fall into two categories: those employing a thermal element such as a bimetallic strip, and those employing electromagnetic devices. Certain existing circuit breakers employ a thermal element to trip the contact mechanism after a time delay under moderate overcurrent conditions, and an electromagnetic device to open the contacts under severe overcurrent conditions. The thermal element has, however, the particular disadvantage that its characteristics are affected by variations in ambient temperature, making its operation unpredictable to some degree.
The hydraulic magnetic circuit breaker provides an inverse time delay under moderate overcurrent conditions, that is, the delay in tripping the contact mechanism is inversely related to the magnitude of the overload. This type of circuit breaker is not unduly affected by variations in ambient temperature. At present, however, such circuit breakers cannot react very quickly to severe overcurrent conditions.
It is an object of the invention to provide a circuit breaker which includes the advantages of present hydraulic magnetic circuit breakers and which can react quickly to severe overcurrent conditions.